The invention relates to a bituminous composition comprising a blend of bitumen, a polyolefin and a thermoplastic elastomer. More particularly, the invention relates to a bituminous composition comprising a blend of bitumen, a polyolefin and a thermoplastic elastomer containing at least two polymer blocks wherein one of said polymer blocks is a crystalline polymer block having a Tm above 40.degree. C. and one of said polymer blocks is an amorphous polymer block having a Tg of 0.degree. C. or lower.
Bituminous materials especially asphalt have long been utilized in roofing materials particularly in built up roofing (i.e. BUR) application, as road paving materials and as adhesive materials. Unfortunately, however, such materials tend to deteriorate under conditions of extreme temperature variations, constant exposure to physical stress and environmental weathering.
In order to overcome the deficiencies of these bituminous materials particularly asphalt, those active in this field have proposed blending various polymers particularly polyolefins and elastomeric polymers with the asphalt.
However, polyolefin modified asphalts suffer from a number of significant disadvantages which materially limit their usefulness. Thus, the polyolefins tend to stiffen the resulting composition which often results in poor low temperature flexibility and low elongations at break which in turn causes the material to become brittle upon exposure to low temperatures and consequently subject to cracking. Moreover, the polyolefin modified asphalts generally have high softening points, e.g. 140.degree. to 150.degree. C., which prevents them from being seamed or adhered to the roof surface by means of the so-called "hot mopping" procedure. In that procedure, the roof surface is mopped with hot asphalt as a roll or sheet of polymer modified asphalt is being applied to the roof. When using the hot mopping procedure, it is necessary that the polymer modified asphalt soften when brought into contact with the hot asphalt in order to produce a strong bond to the roof surface. However, in the case of polyolefin modified asphalts this does not occur because of the materials high softening point. Accordingly, in order to adhere polyolefin modified asphalts to the roof surface, it is necessary to utilize a torching procedure in which a propane torch is used to soften the surface of the modified asphalt as it is being applied to the roof surface. As will be evident, such a torching procedure is both cumbersome and time consuming. Additionally, polyolefins have only very limited compatability with asphalt and as a consequence the resulting composition upon exposure to heat tends to undergo phase separation into a hard asphaltene rich phase and a softer polyolefin rich phase; a situation which results in the composition having lower than desirable properties.
Unsaturated elastomers or elastomeric polymers such as polybutadiene and random butadiene-styrene copolymers have also been blended with asphalt. However, it has been found that in addition to deficiencies in dimensional stability such unsaturated polymers are susceptible to oxidation particularly when exposed to high temperatures and as a result lose many of their desirable properties such as flexibility and strength.
More recently, those active in the bituminous material field have proposed blending hydrogenated butadiene-styrene random copolymers, butadiene-styrene block copolymers and hydrogenated butadiene-styrene block copolymers with asphalt as shown by the following patents:
U.S. Pat. No. 3,856,732 to Bresson et al., relates to a modified asphalt hydraulic sealer which comprises a cut back asphalt and a small amount (e.g. 1 to 10%) of a butadiene-styrene block copolymer of the SBS type, a hydrogenated random butadiene-styrene copolymer or mixtures thereof or an ethylene-vinyl acetate copolymer.
U.S. Pat. No. 3,978,014, to Van Beem et al., relates to bituminous compositions comprising: (a) 95%-75% by weight of a bituminous component Q having an aromaticity exceeding 0.004.times.P+0.280 in which P is the N-heptane asphaltene content, (b) 4%-15% by weight of a block copolymer, M.sub.1, preferably a polystyrene-polyalkadiene-polystyrene; and (c) 4%-15% by weight of a thermoplastic polymer, M.sub.2, different from M.sub.1 and which has a molecular weight above 10,000, a solubility parameter of 7.8-8.8 and a crystallinity below 60% at 25.degree. C. The patent discloses at column 1, lines 46-55 and column 2, lines 48-57 that the block copolymer, M.sub.1 is of the general formula A-B-A in which the A's represent the same or different thermoplastic non-elastomeric polymer blocks prepared by polymerization of one or more monoalkenyl aromatics and in which B represents an elastomeric polymer block prepared either by polymerization of one or more conjugated alkadienes or by copolymerization of one or more conjugated alkadienes with one or more monovinyl aromatics. At column 1, lines 53-55, the patent further discloses that polymer block B may be completely or partly hydrogenated, if desired.
U.S. Pat. No. 4,032,491 to Schoenke relates to a roofing composition for producing a roofing membrane having good bond strength, resistance to cracking, tensile strength and hardness, comprising 5%-40% of asphalt and 60%-95% of a block copolymer of the A-B-A type in which each end block A is formed from a vinyl aromatic monomer and midblock B is a hydrogenated polydiene or a polymer of the ethylene/propylene or ethylene/butylene type. As will be evident, the roofing composition of this patent is basically a block copolymer based composition rather than an asphalt based composition.
U.S. Pat. No. 4,102,849 to Bouton et al., relates to oil-extended hydrogenated diblock copolymers comprising 10-200 parts of oil per 100 parts of a hydrogenated diblock copolymer comprising one block of polybutadiene and one block of a random copolymer of a vinyl arene, such as styrene, and butadiene. The patent, at column 6 lines 53-58, states that the oil-extended hydrogenated diblock copolymers may be utilized for a wide variety of molding operations particularly for rubber hose, shoe soles, tires, industrial and automotive goods, etc. The patent, at column 6 lines 63-68; further discloses that the oil-extended hydrogenated diblock copolymers may be modified by the presence of asphalt, wax, polyvinyl compounds such as polystyrene, ordinary polymers of alpha-olefins such as polypropylene or polyethylene or may be mixed with either natural or synthetic rubbers such as polyisoprene and polybutadiene. This patent also appears to be a block copolymer based composition rather than a bitumen- or asphalt-based composition.
U.S. Pat. No. 4,196,115 to Bresson relates to bituminous or asphalt-based roofing or waterproofing compositions having desirable high and low temperature properties which comprise bitumen or asphalt, at least one radial conjugated diene/monovinyl aromatic copolymer having a weight average molecular weight (Mw) of above 200,000 and a conjugated diene/monovinyl aromatic ratio of 50/50 to 85/15 and at least another or second type radial or linear conjugated diene/monovinyl aromatic copolymer having an Mw of below 200,000 and having the same ratios of conjugated diene/vinyl aromatic. As disclosed in the patent, the conjugated diene/vinyl aromatic copolymers are block copolymers represented by the formula (A-B-A).sub.x Y or (A-B).sub.x Y wherein A represents a non-elastomeric poly(monovinyl aromatic) block containing 8-18 carbon atoms per molecule, and B represents an elastomeric poly (conjugated diene) block containing 4-12 carbon atoms per molecule, Y is at least one atom derived from a polyfunctional treating agent and x represents the number of functional groups of said polyfunctional treating agent and is an integer equal to at least 3.
U.S. Pat. No. 4,610,902 to Eastman et al., relates to a laminate composition useful as a roofing membrane comprising a top and a bottom layer of plastic film bonded together by a modified bitumen material, the top layer of said laminate either containing or being surface coated with an ultraviolet light resistant and absorbing agent. As set forth in the patent, the modified bitumen material is formed by blending a thermoplastic elastomer or thermoplastic rubber or a polyurethane into the bitumen. Thermoplastic elastomers or thermoplastic rubbers disclosed in the patent are styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS) and styrene-ethylene-butylenestyrene (SEBS) block copolymers.
Bituminous compositions comprising bitumen, an elastomer and a polyolefin have also been proposed as shown by the following patents:
U.S. Pat. No. 4,282,127, to Desgouilles, relates to a bitumen - based composition comprising a ternary mixture of (a) 52-78 weight % of bitumen, (b) 20-40 weight % polyolefin and (c) 2-8 weight % of a butadiene-styrene copolymer. As set forth in the patent, the butadiene-styrene copolymer may be a random copolymer or a block copolymer with triblock styrene-butadiene-styrene copolymers being particularly suitable.
U.S. Pat. No. 4,659,759 to Jevanoff et al. relates to a bituminous composition which comprises bitumen and a modifier comprising a polyolefin component and an elastomeric component. According to the patent, the polyolefin component contains polyethylene and polypropylene and the elastomeric component comprises an ethylene-propylene copolymer having a broad compositional distribution with regards to its ethylene content.
Bituminous compositions which have been modified with unsaturated elastomers or elastomeric polymers such as polybutadiene, random butadiene-styrene copolymers or block copolymers of the SBS type as described in several of the aforementioned patents exhibit a number of desirable properties including good low temperature flexibility and high temperature creep resistance properties. However, such compositions exhibit the significant disadvantage that the unsaturated polymers utilized therein are susceptible to oxidation upon exposure to high temperatures which results in deterioration and loss of their desirable properties such as flexibility and strength. Moreover, bituminous compositions modified with SBS block copolymers often vary in properties and compatibility or homogeneity depending upon the nature and type of bitumen which is blended with the SBS block copolymer.
Bituminous compositions which have been modified with hydrogenated random copolymers of butadiene and styrene and hydrogenated SBS type block copolymers as described in several of the above patents exhibit a number of desirable properties including good low temperature flexibility and high temperature creep resistance properties. However, such compositions also have certain disadvantages. Thus, such compositions are generally deficient in solvent resistance. Moreover, bituminous compositions modified with hydrogenated SBS block copolymers often vary in properties and compatibility or homogeneity depending upon the nature and type of bitumen which is blended with the hydrogenated SBS block copolymer.
Accordingly, there remains a need for bituminous compositions which provide a combination of desirable properties including good low temperature and high temperature properties, weathering resistance, dimensional stability, solvent resistance, uniformity of properties and homogeneity.